A digitizer circuit is used to digitize an electrical waveform by performing a transformation from an analog to a digital format in order that storage in memory and subsequent data manipulation may be facilitated by the use of digital circuitry. It is known in the prior art, as exemplified by the Hewlett-Packard Model 1150A waveform analyzer, to perform such digitization by sampling a waveform a fixed number of times over a sample window or user-defined width. A disadvantage of such a prior art digitizer is the inability to depict the location on the waveform of the sample window prior to digitization.
The present invention is directed to a digitizer circuit which digitizes a waveform displayed upon a cathode ray tube (CRT) by sampling the output of the CRT vertical amplifier. The user specifies the sample location by specifying the offset between the CRT trigger signal and the first sample, the width of the sample window, and the number of samples to be taken. From these user-specified parameters of microprocessor is used to determine and implement the necessary delay between the CRT trigger signal and each sample taken by a sample-and-hold circuit.
An advantage of the present invention is the high degree of flexibility the user is permitted in defining an arbitrary portion of the displayed waveform as the sample window. Another advantage is the ability to depict the sample window as an intensified portion of the displayed waveform, thereby allowing the user to view the sample window in relation to the entire displayed waveform prior to digitization.